Deadline servers as a realtime throttling replacement

Posted Jun 18, 2023 17:33 UTC (Sun) by alison (subscriber, #63752)
In reply to: Deadline servers as a realtime throttling replacement by farnz
Parent article: Deadline servers as a realtime throttling replacement

>If that happens, we want it to be possible for the admin to access the system and take corrective action using their normal tools.

What we really want is for the scheduler to manage the system in a latency-sensitive but efficient way, possibly also considering power usage. If a human ever has to login to fix something, we have hard-failed.

Deadline servers as a realtime throttling replacement

Posted Jun 19, 2023 11:31 UTC (Mon) by farnz (subscriber, #17727) [Link]

I don't think that's a useful way to view things; if I, as the admin, accidentally run for(;;) {} as a SCHED_FIFO process at maximum priority, I've told the system that the most important thing to do is to busy-loop, and that busy-looping should take priority over any other work.

This is clearly a bug, and as admin I've clearly made a mistake doing this. But I need some way to recover from this mistake, short of pulling the power out and hoping that I've not accidentally set this up to busy-loop on boot; this is the whole case for throttling, since the scheduler cannot distinguish a busy-loop that stops me doing real work from a hard real time task that really does need 99% of my CPU to meet its deadlines.